Phenomenological Theory of the Molecular Absorption and Dispersion of Sound in Fluids and the Relation between the Relaxation Time of the Internal Energy and the Relaxation Time of the Internal Specific Heat

Abstract

Molecular absorption and dispersion formulas applicable for both liquids and gases have been derived in a phenomenological manner. It was pointed out that the relaxation time of the molecular internal energy τ must be distinguished from the relaxation time of the internal specific heat β and the relation between these two quantities was discussed in detail. The relaxation time τ has the advantage of making the dispersion formula simpler and directly comparable with the dispersion formulas in other cases, such as the relaxation of shear viscosity. The relaxation time β on the other hand, is more closely related with the collision excitation probability of the molecules than τ.